Endogenous Metabolite

Endogenous metabolites refer to the collective set of small-molecule chemical substances present within organelles, cells, organs, biological fluids, or entire organisms; their molecular weights are typically less than 1500 Da. These endogenous metabolites—including lipids, amino acids, short peptides, nucleic acids, carbohydrates, alcohols, and organic acids—not only participate in signal transduction governing genomic function but also receive upstream signals from the environment, thereby bridging the interrelationships among genotype, environment, and phenotype. Based on their biological functions, microbial endogenous metabolites can be broadly classified into two categories: primary metabolites and secondary metabolites. Primary metabolites are the core molecules essential for supporting microbial growth and proliferation; they serve to provide energy to the microbes or act as precursors and cofactors for the synthesis of biological macromolecules. In contrast, microbial secondary metabolites are a class of low-molecular-weight products that are not strictly essential for microbial growth. Nevertheless, microbial secondary metabolites include numerous substances—such as antibiotics, anti-tumor agents, and cholesterol-lowering agents—that are of critical importance to human health^[1][2][3]. Furthermore, the metabolome of a biological organism is influenced by a variety of endogenous factors, including age, sex, body composition, genetic background, and underlying pathological states. The small-molecule metabolites within an organism are diverse and highly distinct; their levels are typically subject to the synergistic regulation of a vast array of enzymes and transport proteins, undergoing processes of synthesis, transformation, degradation, and compartmentalized distribution. Metabolomics research based on endogenous metabolites has been widely applied in the fields of metabolic disorders, neurodegenerative diseases, cancer, cardiovascular diseases, and infectious diseases, where these metabolites hold potential utility as biomarkers or therapeutic targets^[1][2][3].